Image fixing unit for an image forming apparatus

Abstract

An image fixing unit for use in an image forming apparatus for fixing a toner image on a printable medium is provided. The image fixing unit includes a heat roller in which a heater is mounted, a circulating belt tightly engaged with the heat roller and forming a nip through which a printable medium passes, a plurality of guide rollers supporting the circulating belt for rotation of the circulating belt, and bushings formed on both ends of each guide roller and having a regulating portion for preventing the circulating belt from meandering. Protrusions are formed on a surface of the bushings contacting the circulating belt to reduce a contact area between the circulating belt and the bushings. Therefore, the contact area between the traveling circulating belt and the bushings, which are fixed components of the guide rollers, is reduced and wear and tear of the circulating belt and a drive torque for driving the image fixing unit are also thus reduced.

1 . An image fixing unit for use in an image forming apparatus, comprising:
 a heat roller in which a heater is mounted;   a circulating belt engaged with the heat roller, and forming a nip through which a printable medium passes; and   a plurality of guide rollers arranged to support the circulating belt to rotate along with the heat roller,   wherein a protrusion is formed on a surface outside a body of the guide roller, the surface contacting with the circulating belt, when the circulating belt is rotated.   
     
     
         2 . The image fixing unit as claimed in  claim 1 , wherein bushings, which include a regulating portion for preventing the circulating belt from meandering, are mounted on both ends of each guide roller and the surface on which the protrusion is formed is a surface of the bushings. 
     
     
         3 . The image fixing unit as claimed in  claim 2 , wherein a plurality of protrusions are formed on the surface of the bushings contacting the circulating belt to reduce a contact area between the circulating belt and the guide rollers, and wherein each protrusion is formed in a dome shape. 
     
     
         4 . The image fixing unit as claimed in  claim 3 , wherein the protrusions satisfy an equation “0.05 mm≦R 1 ≦R 2 ”, where R 1  indicates a radius of curvature of the protrusions taken along a shaft direction of the guide roller, and R 2  indicates a radius of curvature of the protrusions taken along a traveling direction of the circulating belt. 
     
     
         5 . The image fixing unit as claimed in  claim 3 , wherein the plurality of protrusions are not aligned in lines in a shaft direction of the guide rollers, but are disposed in a zig-zag pattern. 
     
     
         6 . The image fixing unit as claimed in  claim 1 , wherein a space is formed in the protrusion and a ball is rotatably formed in the space of the protrusion. 
     
     
         7 . The image fixing unit as claimed in  claim 1 , wherein the protrusion is formed in a ring shape around an outer circumference of the surface outside the body of the guide roller. 
     
     
         8 . An image forming apparatus comprising:
 a developing unit to develop a toner image and transfer the toner image onto a printable medium; and   an image fixing unit arranged to fix the transferred toner image on the printable medium by heat and pressure, the image fixing device comprising:
 a heat roller in which a heater is mounted; 
 a circulating belt engaged with the heat roller and forming a nip through which the printable medium passes; and 
 a plurality of guide rollers arranged to support the circulating belt to rotate along with the heat roller, 
 wherein a protrusion is formed on a surface outside a body of the guide roller, the surface contacting with the circulating belt when the circulating belt is rotated. 
   
     
     
         9 . The image forming apparatus as claimed in  claim 8 , wherein bushings, which include a regulating portion for preventing the circulating belt from meandering, are mounted on both ends of each guide roller and the surface on which the protrusion is formed is a surface of the bushings. 
     
     
         10 . The image forming apparatus as claimed in  claim 9 , wherein a plurality of protrusions are formed on the surface of the bushings contacting the circulating belt to reduce a contact area between the circulating belt and the guide rollers, and wherein each protrusion is formed in a dome shape. 
     
     
         11 . The image forming apparatus as claimed in  claim 10 , wherein the protrusions satisfy an equation “0.05 mm≦R 1 ≦R 2 ”, where R 1  indicates a radius of curvature of the protrusions taken along a shaft direction of the guide roller and R 2  indicates a radius of curvature of the protrusions taken along a traveling direction of the circulating belt. 
     
     
         12 . The image forming apparatus as claimed in  claim 10 , wherein the plurality of protrusions are not aligned in lines in a shaft direction of the guide rollers, but are disposed in a zig-zag pattern. 
     
     
         13 . The image forming apparatus as claimed in  claim 8 , wherein a space is formed in the protrusion and a ball is rotatably formed in the space of the protrusion. 
     
     
         14 . The image forming apparatus as claimed in  claim 8 , wherein the protrusion is formed in a ring shape around an outer circumference of the surface outside the body of each of the guide rollers. 
     
     
         15 . The image fixing unit as claimed in  claim 1 , wherein the guide rollers are provided with bushings coupled to both end portions of the guide rollers and fixed to the image forming apparatus to support the guide rollers, and regulating portions formed at both end portions of the guide rollers to prevent the circulating belt from meandering over the bushings. 
     
     
         16 . The image fixing unit as claimed in  claim 15 , wherein a plurality of protrusions are formed on part of surfaces of the bushings that are in contact with the circulating belt, adjacent to surfaces of main bodies of the guide rollers which rotate along with the circulating belt. 
     
     
         17 . The image fixing unit as claimed in  claim 16 , wherein each of the protrusions has one of a dome shape, an elliptical dome shape, a cylindrical shaped body with a domed top, and a rectangular shaped body with a domed top. 
     
     
         18 . The image forming apparatus as claimed in  claim 8 , wherein the guide rollers are provided with bushings coupled to both end portions of the guide rollers and fixed to the image forming apparatus to support the guide rollers, and regulating portions formed at both end portions of the guide rollers to prevent the circulating belt from meandering over the bushings. 
     
     
         19 . The image forming apparatus as claimed in  claim 18 , wherein a plurality of protrusions are formed on part of surfaces of the bushings that are in contact with the circulating belt, adjacent to surfaces of main bodies of the guide rollers which rotate along with the circulating belt. 
     
     
         20 . The image forming apparatus as claimed in  claim 19 , wherein each of the protrusions has one of a dome shape, an elliptical dome shape, a cylindrical shaped body with a domed top, and a rectangular shaped body with a domed top. 
     
     
         21 . An image forming apparatus comprising:
 a developing unit arranged to develop a toner image and transfer the toner image onto a printable medium; and   an image fixing unit arranged to fix the transferred toner image on the printable medium by heat and pressure, the image fixing device comprising:   a heat roller in which a heater is mounted;   a circulating belt arranged to cyclically rotate along with the heat roller, and form a nip through which the printable medium passes through when engaged with the heat roller;   guide rollers arranged to support the circulating belt and provided with main bodies to rotate along with the heat roller;   bushings coupled to both end portions of the guide rollers and fixed to support the guide rollers;   regulating portions formed at both end portions of the guide rollers to prevent the circulating belt from meandering over the bushings; and   a plurality of protrusions formed on part of surfaces of the bushings that are in contact with the circulating belt, adjacent to surfaces of main bodies of the guide rollers which rotate along with the circulating belt.   
     
     
         22 . The image forming apparatus as claimed in  claim 21 , wherein the protrusions satisfy an equation “0.05 mm≦R 1 ≦R 2 ”, where R 1  indicates a radius of curvature of the protrusions taken along a shaft direction of the guide roller and R 2  indicates a radius of curvature of the protrusions taken along a traveling direction of the circulating belt. 
     
     
         23 . The image forming apparatus as claimed in  claim 21 , wherein the plurality of protrusions are not aligned in lines in a shaft direction of the guide rollers, but are disposed in a zig-zag pattern. 
     
     
         24 . The image forming apparatus as claimed in  claim 21 , wherein each of the protrusions is provided with a space and a ball is rotatably formed in the space of the protrusion. 
     
     
         25 . The image forming apparatus as claimed in  claim 21 , wherein each of the protrusions is formed in a ring shape around an outer circumference of the surface outside the main body of each of the guide rollers. 
     
     
         26 . The image forming apparatus as claimed in  claim 21 , wherein each of the protrusions has one of a dome shape, an elliptical dome shape, a cylindrical shaped body with a domed top, and a rectangular shaped body with a domed top.